|FINAL DIAGNOSIS:||PALISADED MYOFIBROBLASTOMA (INTRANODAL HEMORRHAGIC SPINDLE-CELL TUMOR WITH "AMIANTHOID" FIBERS)|
This unusual benign primary mesenchymal neoplasm of lymph nodes was described simultaneously by two groups, and termed "palisaded myofibroblastoma" by Weiss at al 1, and "intranodal hemorrhagic spindle-cell tumor with amianthoid fibers" by Suster and Rosai 2. Similar neoplasms have previously been reported as intranodal schwannomas 3.
All of the original twenty-eight cases occured in inguinal lymph nodes. Since then, submandibular and mediastinal locations have been reported. Patients typically present with a solitary, painless, palpable mass. Adults of all ages, and both sexes, are equally affected.
On gross examination, they are typically well-circumscribed round-oval masses, with central firm gray-white tissue, surrounded by hemorrhage and compressed remaining lymph node.
Histologically, low power examination may highlight remaining compressed lymph node separated from the neoplasm by a thick band of sclerotic hyalinized tissue, forming a pseudocapsule. Hemorrhage is a prominent feature. The neoplastic cells are arranged in short interlacing and criss-crossing fascicles, or in palisades which may simulate the Verocay bodies of schwannomas. Perhaps most striking , specific, and aesthetically pleasing are the stellate shaped collagen-rich cores observed in most cases. The dense collagen which comprises these structures has been likened to "amanthoid fibers", giant collagen fibrils named for they're asbestos-like quality, which may be found in degenerative and neoplastic conditions of cartilage 4,5. However, ultractructural studies show that they are formed of collagen fibrils of conventional diameter.
Immunohistochemistry supports the contention that the tumor is of myofibroblastic origin. Cytoplasmic immunoreactivity is reported with smooth muscle actin, myosin, and vimentin antibodies, but not with desmin - a pattern which recapitulates the immunophenotype of normal myofibroblasts. Smooth muscle differentiation, in contrast, is typically accompanied by desmin positivity. Further supporting the myofibroblastic origin of this tumor is the overwhelming preponderance of cases involving inguinal lymph nodes - a site in which abundant actin-positive, desmin-negative, intranodal myofibroblasts is the norm. By comparison, lymph nodes at other locations contain few similar cells 6.
If one is unfamiliar with its features, the neoplasm may be mistaken for a metastatic melanoma or sarcoma. In particular, Kaposi's sarcoma may be suggested by the intranodal location, bands of spindle cells, and prominent hemorrhage . However, Kaposi's sarcoma typically shows greater nuclear pleomorphism, higher mitotic activity, and features slit-like vascular spaces and extracellular eosinophilic bodies. Immunohistochemistry will further distinguish the cells of Kaposi's sarcoma, which are positive with vascular markers, but not with smooth-muscle actin. Negative reactions with S-100 and HMB45 excludes metastatic melanoma.
The neoplasm appears to be benign. In the largest series available 1, sixteen of twenty-two (16/22) patients were alive and well without evidence of disease at follow-up times ranging from ten months to sixteen years (mean 78 months). The remaining six index patients were lost to follow-up, or deceased of unrelated causes. Metastases have not been reported. Our patient is without evidence of disease, two months post-operatively.
Contributed by Rebecca Crowley, M.D., Roger A Hawkins, M.D., and Uma Rao, M.D.